tor/doc/spec/proposals/172-circ-getinfo-option.txt

Filename: 172-circ-getinfo-option.txt
Title: GETINFO controller option for circuit information
Author: Damian Johnson
Created: 03-June-2010
Status: Accepted

Overview:

    This details an additional GETINFO option that would provide information
    concerning a relay's current circuits.

Motivation:

    The original proposal was for connection related information, but Jake make
    the excellent point that any information retrieved from the control port
    is...
    
      1. completely ineffectual for auditing purposes since either (a) these
      results can be fetched from netstat already or (b) the information would
      only be provided via tor and can't be validated.
      
      2. The more useful uses for connection information can be achieved with
      much less (and safer) information.
    
    Hence the proposal is now for circuit based rather than connection based
    information. This would strip the most controversial and sensitive data
    entirely (ip addresses, ports, and connection based bandwidth breakdowns)
    while still being useful for the following purposes:

    - Basic Relay Usage Questions
    How is the bandwidth I'm contributing broken down? Is it being evenly
    distributed or is someone hogging most of it? Do these circuits belong to
    the hidden service I'm running or something else? Now that I'm using exit
    policy X am I desirable as an exit, or are most people just using me as a
    relay?

    - Debugging
    Say a relay has a restrictive firewall policy for outbound connections,
    with the ORPort whitelisted but doesn't realize that tor needs random high
    ports. Tor would report success ("your orport is reachable - excellent")
    yet the relay would be nonfunctional. This proposed information would
    reveal numerous RELAY -> YOU -> UNESTABLISHED circuits, giving a good
    indicator of what's wrong.

    - Visualization
    A nice benefit of visualizing tor's behavior is that it becomes a helpful
    tool in puzzling out how tor works. For instance, tor spawns numerous
    client connections at startup (even if unused as a client). As a newcomer
    to tor these asymmetric (outbound only) connections mystified me for quite
    a while until until Roger explained their use to me. The proposed
    TYPE_FLAGS would let controllers clearly label them as being client
    related, making their purpose a bit clearer.

    At the moment connection data can only be retrieved via commands like
    netstat, ss, and lsof. However, providing an alternative via the control
    port provides several advantages:

      - scrubbing for private data
          Raw connection data has no notion of what's sensitive and what is
          not. The relay's flags and cached consensus can be used to take
          educated guesses concerning which connections could possibly belong
          to client or exit traffic, but this is both difficult and inaccurate.
          Anything provided via the control port can scrubbed to make sure we
          aren't providing anything we think relay operators should not see.
     
      - additional information
          All connection querying commands strictly provide the ip address and
          port of connections, and nothing else. However, for the uses listed
          above the far more interesting attributes are the circuit's type,
          bandwidth usage and uptime.
     
      - improved performance
          Querying connection data is an expensive activity, especially for
          busy relays or low end processors (such as mobile devices). Tor
          already internally knows its circuits, allowing for vastly quicker
          lookups.
     
      - cross platform capability
          The connection querying utilities mentioned above not only aren't
          available under Windows, but differ widely among different *nix
          platforms. FreeBSD in particular takes a very unique approach,
          dropping important options from netstat and assigning ss to a
          spreadsheet application instead. A controller interface, however,
          would provide a uniform means of retrieving this information.

Security Implications:

    This is an open question. This proposal lacks the most controversial pieces
    of information (ip addresses and ports) and insight into potential threats
    this would pose would be very welcomed!

Specification:

   The following addition would be made to the control-spec's GETINFO section:

  "rcirc/id/<Circuit identity>" -- Provides entry for the associated relay
    circuit, formatted as:
      CIRC_ID=<circuit ID> CREATED=<timestamp> UPDATED=<timestamp> TYPE=<flag>
        READ=<bytes> WRITE=<bytes>

    none of the parameters contain whitespace, and additional results must be
    ignored to allow for future expansion. Parameters are defined as follows:
      CIRC_ID - Unique numeric identifier for the circuit this belongs to.
      CREATED - Unix timestamp (as seconds since the Epoch) for when the
          circuit was created.
      UPDATED - Unix timestamp for when this information was last updated.
      TYPE - Single character flags indicating attributes in the circuit:
          (E)ntry : has a connection that doesn't belong to a known Tor server,
            indicating that this is either the first hop or bridged
          E(X)it : has been used for at least one exit stream
          (R)elay : has been extended
          Rende(Z)vous : is being used for a rendezvous point
          (I)ntroduction : is being used for a hidden service introduction
          (N)one of the above: none of the above have happened yet.
      READ - Total bytes transmitted toward the exit over the circuit.
      WRITE - Total bytes transmitted toward the client over the circuit.

  "rcirc/all" -- The 'rcirc/id/*' output for all current circuits, joined by
    newlines.

   The following would be included for circ info update events.

4.1.X. Relay circuit status changed

  The syntax is:
     "650" SP "RCIRC" SP CircID SP Notice [SP Created SP Updated SP Type SP
          Read SP Write] CRLF
     
     Notice =
            "NEW"    / ; first information being provided for this circuit
            "UPDATE" / ; update for a previously reported circuit
            "CLOSED"   ; notice that the circuit no longer exists
    
  Notice indicating that queryable information on a relay related circuit has
  changed. If the Notice parameter is either "NEW" or "UPDATE" then this
  provides the same fields that would be given by calling "GETINFO rcirc/id/"
  with the CircID.